NEXUS-6164: Expose SSL cert check lax options

ConnectionInfo now carries flags about relaxing the
X509 hostname check and SSL certificate check,
thus it's possible to make Nexus client accept
self signed certificates and certificates with
different X509 hostname that the name of the
host it connects to.

Also, client used default connection manager
(usable in single thread environment), but this
time it's set explicitly and made to honor
JSSE system properties, allow greater customization.
NEXUS-6176: Describe page reasoning.

Rendering it now as before.
Also, group imple fixed, to retain processing order
in the reasoning map.
Merge remote-tracking branch 'origin/master' into NEXUS-6164-lax-client-ssl
NEXUS-6164: Renames and tweaks
Deprecate Check class

in favor of Guava
Merge remote-tracking branch 'origin/master' into NEXUS-6176-describe-reasoning

Conflicts:
	plugins/basic/nexus-content-plugin/src/main/java/org/sonatype/nexus/content/internal/VelocityContentRenderer.java
NEXUS-6176: Applied comments
NEXUS-6139: Evict unused items deletes permanently.

Seemingly we have duplicated walker processors used by
Maven proxies and everything else. The latter was
already fixed by this PR below:
https://github.com/sonatype/nexus-oss/pull/262

But as Rich detected, the fix was not applied to
Maven repositories.
Undo method check made in 6189ef698a5a37258e93dbfb5367dfa7baeaa216

To keep it still simple, but deprecation still stands.
NEXUS-6176: Simplified code

Applied Stuart's comments.
NEXUS-6139: Fix IT

As originally it expected that files will land in
trash and hence, no empty directory will exist in there.
NEXUS-6164: Fixed UT incomplete mock
Add support for preparing a WebResource before serving for bits which render templates etc and need to be rendered before bytes and/or length can be known.
check state sanity for prepared resource
content-type is nullable handle null case, add assert to make IDEA shut-up
always set content-type, use application/octet-stream for unknown.
add constant for unknown content-type
update docs
NEXUS-6183: Returned stopwatch for outbound logging purposes

As Yammer does not provide clean way to extract the
"last recorded duration" from timer or timer context in
cheap way.
NEXUS-6183: Start stopwatch

As otherwise it would do any much :)